Direct chip attachment (DCA), also known as "flip chip" technology, is well known to those skilled in the art of integrated circuit mounting techniques. In DCA, the integrated circuit chip has a plurality of terminations on its active surface that are interconnected to a corresponding mounting pad arrangement on a substrate. The interconnections typically are made by raised areas of solder, or solder "bumps," between the substrate and the chip that are remelted during a reflow soldering process, or by heating with a laser. Because of the extremely tight spacing of the interconnections, e.g., 0.5 mm, placing the solder bumps requires great precision to avoid shorts and other defects.
One method that has been used to form the raised areas of solder is to electroplate a layer of tin/lead onto a pad arrangement through a laminated dry film plating resist--a time consuming process. Another method screens and reflows a solder paste onto the pad arrangement, unfortunately producing a high defect rate and resultant low yield. Yet another method forms the solder bumps on the chip itself, but this method typically is done by the chip manufacturer and is not practical or available for any but the most expensive of chips. The overall result of these conventional methods of solder bumping is a substantially increased board or chip cost.
Thus, what is needed is a method and apparatus for providing solder bumps for use in DCA technology. The method and apparatus should be inexpensive and fast, and should produce a high quality interconnection. Ideally, the method and apparatus should be compatible with field repair applications as well as factory production applications.